Atherosclerosis is a complex pathological process that results from an interplay of genetic and environmental components. Many human beings develop accelerated atherosclerosis in the absence of known risk factors, and it has been proposed that some individuals may be genetically predisposed to develop atherosclerosis as a result of mechanisms Operating at the level of the arterial wall. Proliferation of smooth muscle cells in the arterial intima is of key importance in the development and growth of atherosclerotic lesions. In the proposed studies the hypothesis to be tested is that genetic susceptibility to atherosclerosis at the artery wall level includes a differential proliferative response of smooth muscle cells manifested through a regulatory molecule heparan sulfate proteoglycan (HSPG). The studies are possible because of the availability of genetically selected atherosclerosis-susceptible White Carneau (WC) and -resistant Show Racer (SR) pigeons. Cultured aortic smooth muscle cells of the WC pigeons demonstrate a greater proliferation capacity than those of SR. Studies of cell surface HSPG have demonstrated reduced HSPG in WC compared to SR cells. The HSPG remaining on the surface of WC have low sulfated octasaccharide and possess a low content of a unique disaccharide containing iduronic acid 2-O-SO3. When WC HSPG are isolated and added to WC or SR smooth muscle cells in culture, a low antiproliferative effect is observed. SR HSPG block the proliferation of SR cells and are less effective in WC cells. The studies proposed are designed to determine the mechanisms that result in reduced HSPG on WC cells. Based on preliminary work, WC cells produce a pool of cell surface HSPG which is transported to the cell surface but rapidly lost. Possible roles of heparanases and proteinases in this loss will be explored in cell culture studies to define a mechanism that may be unique to the WC cells. Through pulse chase and kinetic modeling, the metabolism and cellular pathways involved in the fast-turning-over pool of HSPG will be examined. Studies of oligosaccharides of cell surface HSPG indicated that the reduced antiproliferative effect of HSPG resulted from the alterations in oligosaccharide sequences and secondary modifications (e.g., sulfation and position). Proposed studies will examine the activity of N-deacetylase/N sulfotransferase, the pivotal enzyme in the production of sulfated oligosaccharide blocks in HS to determine if structural variations in the saccharides of WC HS are attributed to differential enzyme activity. The ultimate goal of the proposal is to determine the role of HSPG in relation to smooth muscle cell proliferation in atherosclerosis and conditions such as restenosis following clinical angioplasty.